We have developed a stopped-flow flow cytometer with subsecond resolution to be used in kinetic analysis of cell activation. This instrument is extending the application of flow cytometry to important biological molecules that interact with cell surface receptors or can be linked to beads. The device is making it possible to examine the kinetics of interaction of a variety of macromolecular assemblies. In year 16, we have shown that the stability of sample flow can be improved in the subsecond time frame by using automated syringes to simultaneously control sample flow and sheath flow (Seamer, Kuckuck and Sklar, manuscript acceptable with revision). A new five syringe mixing device has been designed and manufactured to take advantage of this improved stability for kinetic analysis.